1. Field of the Invention
The present invention relates in general to power supplies for electronic devices, and more particularly, but not exclusively, to direct current (DC) uninterruptible power supplies (UPS) configured as intrinsic power transfer switches for use in computing environments.
2. Description of the Related Art
A controlled transfer switch is a common method to disconnect an electrical service and connect an alternate service to a computer system. Switching electrical services is often required when one service is lost and an alternate service is still functional.
FIG. 1 illustrates a conventional power transfer switch 11. Power distribution to electrical loads 13 and 15 from electrical services A and B is managed by a variety of sensor and control equipment, including a sensor 17 to monitor electrical service A, and a sensor 19 to monitor electrical service B. Additional hardware 21 evaluates statuses of the electrical services A and B, and provides the status information to control transfer switch hardware 23, which provides the switching functionality.
For the conventional switch as illustrated in FIG. 1, overt control is required to disconnect one electrical service and connection of another. The switching action can fail at the sensor, evaluation function, switch controller or at switch itself. This decreases availability and reliability of power to vital computer systems.
The sequence and timing of the transfer switch is important to the overall functionality of the system. Two different electrical services cannot be directly connected to the electrical load (computer system) at the same time because of unmatched phase and frequency or greatly differing magnitudes. The switch must first disconnect a failed service, and then connect a functioning electrical service. This creates several failure modes. For example, the switch may fail to disconnect before connecting, the switch may fail to connect after disconnection, or the switch may connect before disconnecting.
In addition to the foregoing, in any conventional switching system there is a delay or dead time associated with the transfer of power. This can create short gaps in power availability that the computer system's power supplies must accommodate.